precision mediump float;
uniform sampler2D u_texture;
varying mediump vec2 v_uv;
void main(void)
{
	float limit=0.5;
	vec3 color = texture2D(u_texture, v_uv).rgb;
	float brightness = 0.5 * color.r + 0.59 * color.g + 0.11 * color.b;
	float val = step(limit, brightness);
	gl_FragColor = vec4(color * val, 1.0);	
}
